The invention relates to a convection and steam oven for food with an oven chamber and an auxiliary chamber partitioned off from this, in which auxiliary chamber a motor-driven radial-action fan is arranged together with several heating elements surrounding the fan, and arranged at the hub of the fan a pre-atomization element rotating with said fan for the atomization of water optionally supplied through a pipe.
Such a convection and steam oven for food is known, for example, from EP 244 538 B 1. In the case where this prior-art oven is operated as a steam oven, a steam atmosphere is formed by virtue of water flowing from the pipe being atomized in two stages and, in this atomized form, being streamed past the heating elements by the radial air flow generated by the fan, causing it to be transformed into the vapour phase. The steam particles are then further entrained by the flow generated by the fan. Final atomization of the water particles still not yet transformed into the vapour phase is performed by the radial action fan. The pre-atomization action according to this prior-art technology is effected by the fact that formed on the rotational axis of the fan is a closed cup element which rotates with the fan. The end of the water supply pipe is located within this cup element. The rotating cup element features a rim portion and an internal surface which extends away from the rim portion in an inverse taper so that a volume of water can collect within the cup, and so that, after the cup has been filled with the water volume, the surplus water flows over the rim so forming a water film which is atomized by the centrifugal force. The water thus pre-atomized then impinges on the ring-arrangement of blades of the radial-action fan where it is further comminuted as explained above.
A convection and steam oven of the same generic species is also known from the Italian utility model 40 052A/90. In contrast to the convection and steam oven described above, in this case an overpressure is built up in the oven chamber so that the steam formed in the auxiliary chamber and distributed around the oven chamber can be superheated. In addition, this increase in pressure in the oven chamber of approx. 5 mbar leads to a more uniform distribution of the steam atmosphere. The pre-atomization element here takes the form of a drum which co-rotates on the shaft of the fan and features, uniformly distributed around its periphery, a number of slot-like oblong holes. The water is supplied from the pipe to the open end of this slotted drum. The water emerging from the pipe is entrained by the air stream sucked from the centre by the radial-action fan, and is guided through the slot-like oblong holes in the drum wall causing the water to be atomized at the slot-like openings. In contrast to the prior-art pre-atomization element according to EP 244 538 B1, here there is not just one water film formed across the rim of a cup. In this latter case, rather, an atomization effect is achieved across the entire length of the oblong holes so that the water droplets thus pre-atomized impinge in an even distribution pattern onto the fan blades. In this case, therefore, better atomization is achieved because, owing to a different pre-atomization principle, the full depth of the radial-action circular fan is utilized.
However, both prior-art constructional forms exhibit the disadvantage that, after a relatively short service time, limescale depositing and clogging occurs, necessitating the need to replace equipment. The limescale becomes deposited predominantly in the outlet area of the pipe, i.e. at the open end of the closed cup or of the slotted drum. Even a modified constructional form which differs from the Italian utility model application, in which the drum exhibits an outwardly extending conical form, provides no remedy to this problem. Depending on the lime content of the water used, the limescale layer which develops may become so thick within a short time that the entire facility is no longer capable of functioning.
A further convection and steam oven of the same generic species is also disclosed in EP 233 535 B. This constructional form features no independently constructed pre-atomization element. In this case, rather, the water is supplied to the hub of the fan. According to the teaching of this patent, the outlet opening of the water supply means is directed radially from the outside onto the hub, and the outlet opening of the water supply means is arranged above the hub. With this arrangement, it is hoped that the water flowing from the outlet opening can fall from above onto the hub rotating with the fan so that it may be atomized by said hub. This prior-art convection and steam oven results in an unsatisfactory pre-atomization effect.
Based on the last-mentioned prior art, the object of the present invention is to further develop a convection and steam oven of the same generic species such that improved pre-atomization of the water to be evaporated is facilitated.